The present invention relates to an air flow meter for detecting an air flow rate, and more particularly to a resistance heating type air flow meter suitable for measurement of an intake air quantity to be sucked into an internal combustion engine.
A conventional thermal type air flow meter for measuring an intake air quantity to be sucked into an internal combustion engine is described in Japanese Patent Laid-open No. Hei 4-186123, for example. In this thermal type air flow meter, a temperature sensing resistor located in an auxiliary passage is electrically connected through a conductive support to a driving circuit provided outside a main passage.
Further, a conventional temperature sensing resistor is described in Japanese-Patent Laid-open No. Hei 2-205721, for example. This temperature sensing resistor has a structure such that lead wires are connected to both ends of a sensing element. Thus, the temperature sensing resistor is electrically connected through the lead wires to an external device.
In the prior art mentioned above, various resistor portions such as a support, welding portion, and wire bonding portion are present between a terminal of the sensing element and the driving circuit. A resistance in such resistor portions is not constant,causing an error in measurement of a temperature of the sensing element or in heat control. In recent years, the detection of an air flow rate with a high accuracy has been demanded, so that an influence of the resistor portions present between the sensing element and the driving circuit is not ignorable. Such a circumstance is not sufficiently considered in the prior art mentioned above.
It is accordingly an object of the present invention to provide a resistance heating type air flow meter and a temperature sensing resistor which can detect an air flow rate with a high accuracy.
According to a first aspect of the present invention, there is provided a resistance heating type air flow meter for measuring an air flow rate by using a heating resistor having a resistor portion and a lead member for electrically connecting the resistor portion to an external device, wherein the lead member comprises a first lead member for supplying a current to the resistor portion and a second lead member for measuring a voltage in the resistor portion. According to a second aspect of the present invention, there is provided a resistance heating type air flow meter for measuring air flow rate by using a heating resistor, wherein the heating resistor has a connector portion having four terminals electrically connected together. Therefore, according to the present invention, an air flow rate can be detected highly accurately without any influence of wires etc.